Cancer immunotherapy has been an attractive target in the multidisciplinary treatment of cancer patients. Cancer immunotherapy can generally be classified as: (a) passive (or adaptive), consisting of administration of cells or antibodies ex vivo, and (b) active, represented by vaccines, which aims at eliciting a specific immune response against tumor-associate antigens (TAAs) (Dougan et al., Annual Review of Immunology, 2009, 27, pp 83-117). Tumor-associate carbohydrate antigens (TACAs) are not only most abundantly and sometimes aberrantly expressed on the surface of cancer cells but also absent or rarely expressed on normal cells, many of which have been characterized for specific types of cancer (Stevanovic, S., Nat. Rev. Cancer, 2002, 2, 514-520; Hakomori et al., Chem. Biol., 1997, 4, 97-104). Thus, it is of great interest to identify TACAs for use in developing efficient cancer vaccines.
Recently, certain TACAs were identified by monoclonal antibodies and mass spectrometry (Shriver et al., Nat. Rev. Drug Disc., 2004, 3, 863-873; Pacino et al. Br. J. Cancer, 1991, 63, 390-398). Many TACAs expressed on cancer cells in the form of glycolipids or glycoproteins have been characterized and correlated to certain types of cancers. (Bertozzi et al., Nat Rev Drug Discovery, 2005, 4, 477-488). The passively administered or vaccine-induced antibodies against these antigens have correlated with improved prognosis.
Monoclonal antibody (mAb) RM2 was established toward disialoganglioside and found to recognize the glycosyl epitope (b1.4-Gal-NAcDSLc4). Research correlates the grade of malignancy with the reactivity of mAb RM2 to prostate cancer cells (Saito et al., Int. J. Cancer, 2008, 123(3), 633-640). RM2 immunoreactivity was also detected in stroma, suggesting the glycoprotein recognized by RM2 may be shed from cancer cells into the surrounding stroma and then released into the bloodstream. Thus, the RM2 antigen may be a promising target for cancer immunotherapy.